A known valve that has a rotatable adjustment element is the FlowCon® SME regulator valve. The SME valve is a self-balancing dynamic flow control valve that is differential pressure independent, with an actuator that is controlled by an input signal. The amount of liquid flowing though the valve is determined by the flow area of a throttling element in the valve. The valve has a housing from which a rotatable adjustment member protrudes. The angular position of the rotatable adjustment member determines the maximum flow area of the throttling element. The actual position of the rotatable adjustment member has to be set accurately so the operator will know the exact maximum flow for the chosen setting and in particular to avoid that the setting is below the actually required setting.
The position of an axially displaceable shaft that is concentric with the rotatable adjustment member and that further is protruding from the latter, determines the actual flow area of the throttling element between a minimum value and the maximum flow area. The axially displaceable shaft is operably connected to the actuator so that the position of the axially displaceable shaft can be determined with a control signal to the actuator.
The maximum flow area is manually set by an operator when the actuator is dismounted from the valve and the rotatable adjustment member can be accessed. The shape and size of the rotatable adjustment member and the torque required to rotate it is such that it is not possible for the operator to adjust it without the use of a tool. For this purpose a special key is provided. The special key can detachably couple to the rotatable adjustment member and provides the operator with enough leverage to adjust the position of the rotatable adjustment member. The surface of the valve around the rotatable adjustment member is provided with a rough angular scale and the rotatable adjustment member is provided with a small indicator arrow for indicating the portion of the rotatable adjustment member relative to the angular scale. Inside the valve a geared mechanism connects the rotatable adjustment member to a counting wheel that is visible next to the angular scale and provides the operator with fine angular position information. After adjusting the rotatable adjustment member to a desired setting the key is detached and the actuator is mounted on the valve and the rotatable adjustment member is no longer accessible.
This known valve and key assembly has proven to function well, but requires a relatively complicated mechanism for indicating the fine angular position of the rotatable adjustment member. This mechanism comprises a relatively large number of parts that is complicated to handle and assemble in the production process. Further, there will always be a certain amount of play due to tolerances in the individual components of the gear mechanism, and these are added up in a gear mechanism with several components in series, which can lead to hysteresis and inaccuracy. In the known valve this aspect is solved by an operator always staring a setting from the minimum setting and increasing from the minimum setting to the desired setting.